The radio communication system according to the related art includes a mobile station (MS) and a base station (BS) providing a service within a cell, which is a predetermined area. The quality of a transmission signal in a radio channel between the mobile station and the base station may be affected by a change in a radio environment. Particularly, the radio channel changes over time due to various forms of surrounding scatters, movement of the mobile station, or the like. In addition, since a reception power is rapidly reduced in accordance with an increase in a distance between radio communications subjects, there is a restriction in the distance. Therefore, the mobile station may generally communicate with the base station when it is within the coverage of the base station. As described above, a maximum transmission speed between the base station and the mobile station, a throughput of users within a cell, and a throughput of all cells are reduced due to factors such as the scatters, a moving speed of the mobile station, a distance of transmitting and receiving devices, or the like. For example, in the case in which the mobile station is positioned at a cell boundary or there is an obstacle such as a building between the mobile station and the base station, the communications quality between the mobile station and the base station may not be good.
One of the solutions for overcoming the above-mentioned problem is to introduce a relay station (RS) into a radio communications system. The relay station indicates a device that relays a signal between the mobile station and the base station. It is expected that effects such as the improvement of the throughput of the radio communications system, the extension of the coverage, or the like, will be accomplished by introducing various technologies capable of compensating for deterioration of the transmission signal between the base station and the mobile station into the relay station.
However, there are considerations in the case in which the relay station is introduced into the radio communications system. For example, there may be a limitation between the base station and the relay station in that specific subframes may not be used for the base station to transmit a signal to the relay station. In the case of using a frequency division duplex (FDD) scheme in the radio communications system, the base station may not transmit the signal to the relay station in the subframes having subframe indices within a radio frame corresponding to 0, 4, 5, and 9. The reason is due to self-interference and the fact that the relay station should transmit essential information to the mobile station connected thereto in the above-mentioned specific subframes. The self-interference is generated because a frequency band in which the relay station receives the signal from the base station is the same as that in which the relay station transmits the signal to a relay user equipment. That is, the relay station should transmit essential signals to the mobile station connected thereto in the subframes having the subframe indices corresponding to 0, 4, 5, and 9, and it is difficult for the relay station to receive the signal from the base station due to the self-interference in the subframes in which it transmits these essential signals.
The above-mentioned limitation may also be problematic in the case in which a hybrid automatic repeat request (HARQ) operation is performed between the base station and the relay station. For example, a case where the base station transmits or retransmits data to the relay station in the subframes in which the transmission from the base station to the relay station is limited may occur.
Therefore, a need exists for a method for allocating subframes in consideration of a limitation that is present in a link between a base station and a relay station in a radio communications system.